Achondroplasia is a disorder of bone growth that causes the most common type of dwarfism.
Causes, incidence, and risk factors: Achondroplasia is one of a group of disorders called chondrodystrophies or osteochondrodysplasias.
Achondroplasia may be inherited as an autosomal dominant trait, which means that if a child gets the defective gene from one parent, the child will have the disorder. If one parent has achondroplasia, the infant has a 50% chance of inheriting the disorder. If both parents have the condition, the infant's chances of being affected increase to 75%.
However, most cases appear as spontaneous mutations. This means that two parents without achondroplasia may give birth to a baby with the condition.
Symptoms: The typical appearance of achondroplastic dwarfism can be seen at birth. Symptoms may include:
- Abnormal hand appearance with persistent space between the long and ring fingers
- Bowed legs
- Decreased muscle tone
- Disproportionately large head-to-body size difference
- Prominent forehead (frontal bossing )
- Shortened arms and legs (especially the upper arm and thigh)
- Short stature (significantly below the average height for a person of the same age and sex)
- Spinal stenosis
- Spine curvatures called kyphosis and lordosis
Signs and tests: During pregnancy, a prenatal ultrasound may show excessive amniotic fluid surrounding the unborn infant.
Examination of the infant after birth shows increased front-to-back head size. There may be signs of hydrocephalus ("water on the brain").
X-rays of the long bones can reveal achondroplasia in the newborn.
Treatment: There is no specific treatment for achondroplasia. Related abnormalities, including spinal stenosis and spinal cord compression, should be treated when they cause problems.
Expectations (prognosis): People with achondroplasia seldom reach 5 feet in height. Intelligence is in the normal range. Infants who receives the abnormal gene from both parents do not often live beyond a few months.
Complications:
- Clubbed feet
- Fluid buildup in the brain (hydrocephalus)
Calling your health care provider: If there is a family history of achondroplasia and you plan to have children, you may find it helpful to speak to your health care provider.
Prevention: Genetic counseling may be helpful for prospective parents when one or both have achondroplasia. However, because achondroplasia most often develops spontaneously, prevention is not always possible.
References: Horton WA, Hecht JT. Disorders involving transmembrane receptors. In: Kliegman RM, Behrman RE, Jenson HB, Stanton BF, eds. Nelson Textbook of Pediatrics. 19th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 687.
